Air conditioner

ABSTRACT

It is an object of the present invention to provide an air conditioner for inhibiting noise increase and heating performance degradation due to frost attachment onto an outdoor heat exchanger. In an air conditioner ( 1 ), a determining part ( 43 ) of a control unit ( 4 ) determines that the amount of frost attaching onto an outdoor heat exchanger ( 13 ) is increased when a difference between an outdoor temperature To and an outdoor heat exchanger temperature Te is increased, and executes a frost attaching condition operation control for reducing the rotation speed of an outdoor fan ( 23 ). The operating frequency of the compressor ( 11 ) is herein increased in accordance with the reduction amount of the temperature of an indoor heat exchanger ( 15 ). The control unit ( 4 ) includes change amounts preliminarily set for changing the operating frequency of the compressor ( 11 ) in stages. The change amounts correspond to the stages on a one-to-one basis. The control unit ( 4 ) increases the operating frequency of the compressor ( 11 ) by corresponding one of the change amounts required for upgrading a present stage of the operating frequency of the compressor ( 11 ) to a stage immediately higher than the present stage every time the temperature of the outdoor heat exchanger ( 15 ) is reduced by a predetermined amount, and reduces the rotation speed of the outdoor fan ( 23 ) in accordance with the change amount.

TECHNICAL FIELD

The present invention relates to an air conditioner.

BACKGROUND ART

In executing a heating operation, the air conditioners are normallyconfigured to execute a control of inhibiting degradation in heatingperformance due to frost attachment onto the outdoor heat exchangersthereof immediately before the start of a defrosting operation. Forexample, Patent Literature 1 (Japan Laid-open Patent ApplicationPublication No. JP-A-S62-069070) describes a control of preventingreduction in the rotation speed of an outdoor fan due to increase inventilation resistance. Specifically, a control unit is hereinconfigured to increase voltage to be inputted into a fan motor forkeeping the rotation speed of the outdoor fan constant, and therebyinhibits reduction in the evaporation temperature of a refrigerant. Thecontrol inhibits increase in the amount of frost attaching onto theoutdoor heat exchanger and prevents degradation in heating performance.

SUMMARY OF THE INVENTION Technical Problem

In employing the control technology described in Patent Literature 1,however, the rotation speed of the outdoor fan is kept constant againstventilation resistance. Therefore, noise is herein obviously increasedcompared to the frost-free conditions. A user or users may feeluncomfortable due to such noise increase.

It is an object of the present invention to provide an air conditionerfor inhibiting noise increase, and simultaneously, inhibiting extremedegradation in heating performance due to frost attachment onto anoutdoor heat exchanger.

Solution to Problem

An air conditioner according to a first aspect of the present inventionis of a type using a vapor compression refrigeration cycle forcirculating a refrigerant sequentially through a compressor, an indoorheat exchanger, a decompressor and an outdoor heat exchanger duringexecution of a heating operation. The air conditioner includes anoutdoor fan and a control unit. The outdoor fan is configured to blowthe outdoor heat exchanger.

The control unit includes a determining part configured to determinewhether or not the amount of frost attaching onto the outdoor heatexchanger is increased during execution of the heating operation. Thecontrol unit is configured to control an operating frequency of thecompressor and a rotation speed of the outdoor fan. Further, the controlunit is configured to: reduce the rotation speed of the outdoor fan whenthe determining part determines that the amount of frost attaching ontothe outdoor heat exchanger is increased; and execute a frost attachingcondition operation control for increasing the operating frequency ofthe compressor either simultaneously with reducing the rotation speed ofthe outdoor fan or when a predetermined performance degradation issubsequently caused after reducing the rotation speed of the outdoorfan.

According to the air conditioner of the first aspect of the presentinvention, noise of the outdoor fan is reduced in response to reductionin the rotation speed of the outdoor fan even when noise is easilyproduced due to frost attachment onto the outdoor heat exchanger duringexecution of the heating operation. Therefore, increase in noise of theentire air conditioner is inhibited. Further, degradation in heatingperformance is inhibited by increasing the operating frequency of thecompressor. It should be noted that noise of the compressor is increasedin accordance with increase in the operating frequency of thecompressor. However, noise of the outdoor fan is herein reduced.Consequently, noise increase is inhibited for the entire airconditioner.

An air conditioner according to a second aspect of the present inventionrelates to the air conditioner according to the first aspect of thepresent invention. In the air conditioner, the control unit isconfigured to reduce the rotation speed of the outdoor fan in accordancewith an increase amount of the operating frequency of the compressorduring execution of the frost attaching condition operation control.

According to the air conditioner of the second aspect of the presentinvention, noise is increased in accordance with the increase amount ofthe operating frequency of the compressor. However, the rotation speedof the outdoor fan is reduced to the extent that the increase amount ofthe noise is cancelled out. Therefore, noise is kept roughly constant inthe entire air conditioner.

An air conditioner according to a third aspect of the present inventionrelates to the air conditioner according to one of the first and secondaspects of the present invention. The air conditioner further includes afirst temperature sensor and a second temperature sensor. The firsttemperature sensor is configured to detect an outdoor temperature, whilethe second temperature sensor is configured to detect a temperature ofthe outdoor heat exchanger. Further, the control unit is configured to:monitor a difference between a value detected by the first temperaturesensor and a value detected by the second temperature sensor; anddetermine that the amount of frost attaching onto the outdoor heatexchanger is increased when the difference is increased.

According to the air conditioner of the third aspect of the presentinvention, it is estimated that the evaporation temperature of therefrigerant is reduced due to frost attachment when the differencebetween the outdoor temperature and the temperature of the outdoor heatexchanger is increased. This is because the difference between theoutdoor temperature and the evaporation temperature of the refrigerantis roughly constant in a frost-free condition of the outdoor heatexchanger during execution of the heating operation. Therefore, it iseasily determined whether or not the amount of frost attaching onto theoutdoor heat exchanger is increased through the monitoring of thedifference between the outdoor temperature and the temperature of theoutdoor heat exchanger.

An air conditioner according to a fourth aspect of the present inventionrelates to the air conditioner according to the third aspect of thepresent invention. The air conditioner further includes a thirdtemperature sensor. The third temperature sensor is configured to detecta temperature of the indoor heat exchanger. Further, the control unit isconfigured to: monitor the temperature of the indoor heat exchangerthrough the third temperature sensor; and increase the operatingfrequency of the compressor in accordance with a reduction amount of thetemperature of the indoor heat exchanger during execution of the frostattaching condition operation control.

According to the air conditioner of the fourth aspect of the presentinvention, degradation in heating performance is expressed as reductionin the condensation temperature during execution of the heatingoperation. Therefore, degradation in heating performance is inhibited byincreasing the operating frequency of the compressor in accordance withthe reduction amount of the temperature of the indoor heat exchanger.

An air conditioner according to a fifth aspect of the present inventionrelates to the air conditioner according to the fourth aspect of thepresent invention. In the air conditioner, the control unit includeschange amounts preliminarily set for changing the operating frequency ofthe compressor in stages. The change amounts correspond to the stages ona one-to-one basis. The operating frequency of the compressor is hereinconfigured to be increased by corresponding one of the change amountsrequired for upgrading a present stage of the operating frequency of thecompressor to a stage immediately higher than the present stage everytime the temperature of the indoor heat exchanger is reduced by apredetermined amount.

According to the air conditioner of the fifth aspect of the presentinvention, multiple stages are set for the operating frequency of thecompressor in order to increase or reduce the operating frequency of thecompressor in stages in accordance with a load during execution of thenormal operation. Further, the stages are designed to be applied to theoperating frequency during execution of the frost attaching conditionoperation control. Therefore, the control design can be easily created.

An air conditioner according to a sixth aspect of the present inventionrelates to the air conditioner according to the third aspect of thepresent invention. The air conditioner further includes a pressuresensor. The pressure sensor is disposed on a discharge side of thecompressor. The pressure sensor is configured to detect a higher sidepressure. Further, the control unit is configured to: monitor the higherside pressure through the pressure sensor; and increase the operatingfrequency of the compressor in accordance with a reduction amount of thehigher side pressure during execution of the frost attaching conditionoperation control.

According to the air conditioner of the sixth aspect of the presentinvention, degradation in heating performance is expressed as reductionin the higher side pressure during execution of the heating operation.Therefore, degradation in heating performance is inhibited by increasingthe operating frequency of the compressor in accordance with thereduction amount of the higher side pressure.

An air conditioner according to a seventh aspect of the presentinvention relates to the air conditioner according to the sixth aspectof the present invention. In the air conditioner, the control unitincludes change amount preliminarily set for changing the operatingfrequency of the compressor in stages. The change amounts correspond tothe stages of the operating frequency of the compressor on a one-to-onebasis. The operating frequency of the compressor is configured to beincreased by corresponding one of the change amounts required forupgrading a present stage of the operating frequency of the compressorto a stage immediately higher than the present stage every time thehigher side pressure is reduced by a predetermined amount.

According to the air conditioner of the seventh aspect of the presentinvention, multiple stages are set for the operating frequency of thecompressor in order to increase or reduce the operating frequency of thecompressor in stages in accordance with load during execution of thenormal operation. Further, the stages are designed to be applied to theoperating frequency of the compressor during execution of the frostattaching condition operation control. Therefore, the control design canbe easily created.

An air conditioner according to an eighth aspect of the presentinvention relates to the air conditioner according to one of the firstto seventh aspects of the present invention. In the air conditioner, thecontrol unit is configured to: count an elapsed time after activation ofthe compressor; and execute a defrosting operation control for resolvingfrost attachment onto the outdoor heat exchanger when the elapsed timereaches a predetermined period of time during execution of the frostattaching condition operation condition while an evaporation temperatureof the refrigerant reaches a predetermined temperature. According to theair conditioner of the eighth aspect of the present invention, the frostattaching condition operation control is executed until immediatelybefore the start of the defrosting operation. This makes a user or usersless likely to feel that heating is insufficient.

Advantageous Effects of Invention

According to the air conditioner of the first aspect of the presentinvention, noise of the outdoor fan is reduced even when noise is easilyproduced due to frost attachment onto the outdoor heat exchanger duringexecution of the heating operation. Therefore, noise increase isinhibited for the entire air conditioner. Further, degradation inheating performance due to frost attachment is inhibited by increasingthe operating frequency of the compressor.

According to the air conditioner of the second aspect of the presentinvention, noise is increased in accordance with the increase amount ofthe operating frequency of the compressor. However, the rotation speedof the outdoor fan is reduced to the extent that the increase amount ofthe noise is cancelled out. Therefore, noise is kept roughly constant inthe entire air conditioner.

According to the air conditioner of the third aspect of the presentinvention, it is easily determined whether or not the amount of frostattaching onto the outdoor heat exchanger is increased through themonitoring of the difference between the outdoor temperature and thetemperature of the outdoor heat exchanger.

According to the air conditioner of the fourth aspect of the presentinvention, degradation in heating performance is expressed as reductionin the condensation temperature during execution of the heatingoperation. Therefore, degradation in heating performance is inhibited byincreasing the operating frequency of the compressor in accordance withthe reduction amount of the temperature of the indoor heat exchanger.

According to the air conditioner of the fifth aspect of the presentinvention, multiple stages are set for the operating frequency of thecompressor in order to increase or reduce the operating frequency of thecompressor in stages in accordance with load during execution of thenormal operation. Further, the stages are designed to be applied to theoperating frequency during execution of the frost attaching conditionoperation control. Therefore, the control design can be easily created.

According to the air conditioner of the sixth aspect of the presentinvention, degradation in heating performance is expressed as reductionin the higher side pressure during execution of the heating operation.Therefore, degradation in heating performance is inhibited by increasingthe operating frequency of the compressor in accordance with thereduction amount of the higher side pressure.

According to the air conditioner of the seventh aspect of the presentinvention, multiple stages are set for the operating frequency of thecompressor in order to increase or reduce the operating frequency of thecompressor in stages in accordance with load during execution of thenormal operation. Further, the stages are designed to be applied to theoperating frequency of the compressor during execution of the frostattaching condition operation control. Therefore, the control design canbe easily created.

According to the air conditioner of the eighth aspect of the presentinvention, the frost attaching condition operation control is executeduntil immediately before the start of the defrosting operation. Thismakes a user or users less likely to feel that heating is insufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an air conditioner according to afirst exemplary embodiment of the present invention.

FIG. 2 includes charts representing relations among outdoor fan input,outdoor fan rotation speed and outdoor fan blowing sound in executing anormal control under a frost attaching condition.

FIG. 3 is an operational flowchart from start of a heating operationcontrol to start of a defrosting operation control.

FIG. 4 is a chart representing relations among elapsed time after startof a heating operation, indoor heat exchanger temperature and compressoroperating frequency.

FIG. 5 is an operational flowchart from start of a heating operationcontrol to start of a defrosting operation control in an air conditioneraccording to a first modification of the present invention.

FIG. 6 is an operational flowchart from start of a heating operationcontrol to start of a defrosting operation control in an air conditioneraccording to a second modification of the present invention.

FIG. 7 is a chart representing relations among elapsed time after startof a heating operation, indoor heat exchanger temperature and compressoroperating frequency in an air conditioner according to a secondexemplary embodiment.

FIG. 8 is a chart representing relations among elapsed time after startof a heating operation, higher side pressure and compressor operatingfrequency in an air conditioner according to a modification of thesecond exemplary embodiment.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will be hereinafterexplained with reference to figures. It should be noted that thefollowing exemplary embodiments are specific examples of the presentinvention and are not intended to limit the technical scope of thepresent invention.

First Exemplary Embodiment

<Air Conditioner Structure>

FIG. 1 is a configuration diagram of an air conditioner according to afirst exemplary embodiment of the present invention. In FIG. 1, the airconditioner 1 includes an outdoor unit 2 and an indoor unit 3. It shouldbe noted that a plurality of the indoor units 3 may be herein provided.

The air conditioner 1 includes a refrigerant circuit 10 filled with arefrigerant. The refrigerant circuit 10 includes an outdoor circuitaccommodated in the outdoor unit 2 and an indoor circuit accommodated inthe indoor unit 3. The outdoor circuit and the indoor circuit areconnected through a gas-side communicating pipe 17 a and a liquid-sidecommunicating pipe 17 b.

<Outdoor Unit Configuration>

A compressor 11, a four-way switching valve 12, an outdoor heatexchanger 13 and an expansion valve 14 are connected to the outdoorcircuit in the outdoor unit 2. A liquid-side closing valve 19 isdisposed in one end of the outdoor circuit, and the liquid-sidecommunicating pipe 17 b is connected thereto. A gas-side closing valve18 is disposed on the other end of the outdoor circuit, and the gas-sidecommunicating pipe 17 a is connected thereto.

The discharge side of the compressor 11 is connected to a first port P1of the four-way switching valve 12. The suction side of the compressor11 is connected to a third port P3 of the four-way switching valve 12via an accumulator 20. The accumulator 20 is configured to separate theliquid refrigerant and the gas refrigerant.

The outdoor heat exchanger 13 is a cross-fin type fin-and-tube heatexchanger. An outdoor fan 23 is disposed in the vicinity of the outdoorheat exchanger 13 in order to supply outdoor air to the outdoor heatexchanger 13. One end of the outdoor heat exchanger 13 is connected to afourth port P4 of the four-way switching valve 12. The other end of theoutdoor heat exchanger 13 is connected to the expansion valve 14functioning as a decompression unit.

The expansion valve 14 is an electronic expansion valve of an openingdegree variable type and is connected to the liquid-side closing valve19. Further, a second port P2 of the four-way switching valve 12 isconnected to the gas-side closing valve 18.

The four-way switching valve 12 is configured to switch between a firststate (a state depicted with a solid line in FIG. 1) and a second state(a state depicted with a dotted line in FIG. 1). In the first state, thefirst port P1 and the fourth port P4 are communicated while the secondport P2 and the third port P3 are communicated. In the second state, thefirst port P1 and the second port P2 are communicated while the thirdport P3 and the fourth port P4 are communicated.

<Indoor Unit Structure>

The indoor circuit is provided with an indoor heat exchanger 15. Theindoor heat exchanger 15 is a cross-fin type fin-and-tube heatexchanger. An indoor fan 33 is disposed in the vicinity of the indoorheat exchanger 15 in order to supply indoor air to the indoor heatexchanger 15.

<Various Sensors>

The air conditioner 1 includes an outdoor temperature sensor 101 formedby a thermistor, an outdoor heat exchanger temperature sensor 102 and anindoor heat exchanger temperature sensor 103. The outdoor temperaturesensor 101 is configured to detect the temperature of the surrounding ofthe outdoor unit 2. The outdoor heat exchanger temperature sensor 102 isattached to the outdoor heat exchanger 13 and is configured to detectthe temperature of the refrigerant flowing through a predeterminedregion of the outdoor heat exchanger 13. Then, a control unit 4 isconfigured to control the operation of the air conditioner 1 based onthe values measured by the aforementioned temperature sensors.

<Air Conditioner Actions>

The operation of the air conditioner 1 can be switched into either thecooling operation or the heating operation through the four-wayswitching valve 12.

(Cooling Operation)

In the cooling operation, the four-way switching valve 12 is set to bein the first state (depicted with the solid line in FIG. 1). When thecompressor 11 is operated under the condition, a vapor compressionrefrigeration cycle is executed in the refrigerant circuit 10. In thiscase, the outdoor heat exchanger 13 is configured to function as acondenser whereas the indoor heat exchanger 15 is configured to functionas an evaporator.

High-pressure refrigerant discharged from the compressor 11 exchangesheat with the outdoor air in the outdoor heat exchanger 13 and isthereby condensed. After passing through the outdoor heat exchanger 13,the refrigerant is decompressed in passing through the expansion valve14. Subsequently, the decompressed refrigerant exchanges heat with theindoor air in the indoor heat exchanger 15 and is thereby evaporated.After passing through the indoor heat exchanger 15, the refrigerant isinhaled into the compressor 11 and is therein compressed.

(Heating Operation)

In the heating operation, the four-way switching valve 12 is set to bein the second state (depicted with the dotted line in FIG. 1). When thecompressor 11 is then operated under the condition, a vapor compressionrefrigeration cycle is executed in the refrigerant circuit 10. In thiscase, the outdoor heat exchanger 13 is configured to function as anevaporator whereas the indoor heat exchanger 15 is configured tofunction as a condenser.

High-pressure refrigerant discharged from the compressor 11 exchangesheat with the indoor air in the indoor heat exchanger 15 and is therebycondensed. The condensed refrigerant is decompressed in passing throughthe expansion valve 14. Subsequently, the decompressed refrigerantexchanges heat with the outdoor air in the outdoor heat exchanger 13 andis thereby evaporated. After passing through the outdoor heat exchanger13, the refrigerant is inhaled into the compressor 11 and is thereincompressed.

<Outdoor Fan>

The outdoor fan 23 includes a motor 23 a. The motor 23 a is a long-lifebrushless DC motor and is configured to execute a duty control.Specifically, the motor 23 a is configured to control an on-time ratioin a power input cycle (i.e., a duty cycle) in order to change therotation speed of the outdoor fan 23. For example, the rotation speed ofthe outdoor fan 23 is reduced when ventilation resistance increases dueto frost attachment onto the outdoor heat exchanger 13. However, powersupply to be inputted into the motor 23 a of the outdoor fan 23 isincreased in proportion to increase in the duty cycle. The rotationspeed of the outdoor fan 23 is accordingly increased.

In the normal control, power supply inputted into the motor 23 a isincreased or reduced for keeping the rotation speed of the outdoor fan23 constant. Specifically, for keeping the rotation speed of the outdoorfan 23 constant, the outdoor fan input is increased or reduced inresponse to increase or reduction in the rotation speed of the outdoorfan 23. FIG. 2 includes charts representing “relations among outdoor faninput, outdoor fan rotation speed and outdoor fan blowing sound inexecuting a normal control under a frost attaching condition”. In thecharts, the horizontal axes, from bottom to top, represent elapsed timeafter start of a heating operation, whereas the vertical axes representoutdoor fan input, outdoor fan rotation speed and outdoor fan blowingsound. When a predetermined period of time TD is elapsed after start ofthe heating operation, frost starts attaching onto the outdoor heatexchanger 13 and ventilation resistance accordingly starts increasing.In the normal control, the outdoor fan input is increased for preventingreduction in the rotation speed due to ventilation resistance andthereby for keeping the rotation speed of the outdoor fan 23 constant.Therefore, blowing sound is acutely increased.

<Operational Flow from Start of Heating Operation Control to Start ofDefrosting Operation Control>

FIG. 3 is an operational flowchart from start of a heating operationcontrol to start of a defrosting operation control. When a heatingoperation is started, the control unit 4 starts counting an elapsed timeTD after the start of the heating operation in Step S1. The processingthen proceeds to Step S2. In Step S2, the control unit 4 keeps a standbystate for a predetermined period of time (TD0) until the rotation speedof the compressor 11 reaches a target rotation speed. The processingthen proceeds to Step S3 and the control unit 4 sets the value of avariable X to be “a”. A value, herein substituted in the variable X, isobtained by adding a predetermined value to the difference between anoutdoor temperature To and an outdoor heat exchanger temperature Te. Itshould be noted that the difference between the outdoor temperature Toand the outdoor heat exchanger temperature Te is constant when theoutdoor heat exchanger 13 is in a frost-free condition. Therefore, thevalue “a” of a temperature slightly higher than the difference is set asthe initial value of the variable X.

In Step S4, the control unit 4 detects the outdoor temperature Tothrough the outdoor temperature sensor 101. The processing then proceedsto Step S5. In Step S5, the control unit 4 detects the outdoor heatexchanger temperature Te through the outdoor heat exchanger temperaturesensor 102. The processing then proceeds to Step S6. In Step S6, thecontrol unit 4 determines whether or not the difference between theoutdoor temperature To and the outdoor heat exchanger temperature Te isgreater than or equal to X.

The processing then proceeds to Step S7 when the control unit 4determines the result in Step S6 as “Yes”. By contrast, the processingreturns to Step S4 when the control unit 4 determines the result in StepS6 as “No”. When the outdoor heat exchanger 13 is in a frost-freecondition, “X=a” remains and therefore a control in Steps S1 to S6,so-called a normal heating operation control, is continued.

In Step S7, the control unit 4 sets the value of the variable X to be avalue obtained by adding a predetermined amount “s” to “To−Te” in StepS6 (i.e., To−Te+s). The processing then proceeds to Step S8. When thedifference between the outdoor temperature To and the outdoor heatexchanger temperature Te is greater than “a”, the evaporationtemperature of the refrigerant is lowered. Therefore, it is determinedthat frost attaches onto the outdoor heat exchanger 13. Subsequently,the control unit 4 resets the value of the variable X every time thedifference between the outdoor temperature To and the outdoor heatexchanger temperature Te is reduced by the predetermined amount “s”.

In Step S8, the control unit 4 determines whether or not the elapsedtime TD after start of the heating operation reaches a predeterminedperiod of time TD1. The processing then proceeds to Step S9 when thecontrol unit 4 determines the result in Step S8 as “Yes”. By contrast,the processing returns to Step S4 when the control unit 4 determines theresult in Step S8 as “No”. To reliably achieve a predetermined level ofoperation efficiency, the control unit 4 herein determines whether ornot “TD>TD1” is true. It should be noted that the operation efficiencyis set as a ratio of a net heating operation time to a total heatingoperation time, where the total heating operation time is set as the sumof the net heating operation time and a defrosting operation time.

In Step S9, the control unit 4 increases the operating frequency of thecompressor 11 by a predetermined amount. The control unit 4 executesStep S9 for preventing degradation in heating performance until theheating operation control is switched into the defrosting operationcontrol after the predetermined period of time TD1 is elapsed forreliably achieving a predetermined level of operation efficiency. Thecontrol unit 4 includes change amounts preliminarily set for changingthe operating frequency of the compressor 11 in stages. The changeamounts herein correspond to the stages on a one-to-one basis. Inincreasing the operating frequency of the compressor 11, the controlunit 4 is configured to increase the operating frequency bycorresponding one of the change amounts required for upgrading thepresent stage of the operating frequency of the compressor 11 to a stageimmediately higher than the present stage.

In Step S10, the control unit 4 reduces the rotation speed of theoutdoor fan 23 by a predetermined amount. The control unit 4 executesStep S10 for cancelling out noise increased in response to increase inthe operating frequency of the compressor 11 by reducing the rotationsound of the outdoor fan 23. Therefore, noise is increased in responseto increase in the operating frequency of the compressor 11, whereasnoise is reduced in response to reduction in the rotation speed of theoutdoor fan 23. Consequently, noise is kept roughly constant in the airconditioner 1.

In Step S11, the control unit 4 determines whether or not the outdoorheat exchanger temperature Te is less than or equal to a predeterminedcalculated value. The processing then proceeds to Step S12 when thecontrol unit 4 determines the result in Step S11 as “Yes”. In Step S12,the control unit 4 starts executing the defrosting operation control. Bycontrast, the processing returns to Step S4 when the control unit 4determines the result in Step S11 as “No”. The predetermined calculatedvalue is a value calculated based on the outdoor temperature To (i.e.,αTo−β+γ). The calculated value is set in consideration of not onlylowering in the outdoor temperature To but also the other factors (e.g.,humidity) as the reasons for frost attachment onto the outdoor heatexchanger 13.

(Relation between Indoor Heat Exchanger Temperature and Increase inCompressor Operating Frequency)

As represented in Steps S4 to S10 of FIG. 3, the control unit 4increases the operating frequency of the compressor 11 and reduces therotation speed of the outdoor fan 23 every time the difference betweenthe outdoor temperature To and the outdoor heat exchanger temperature Teexceeds the predetermined amount “s”. FIG. 4 is a chart representing therelation among elapsed time after start of the heating operation, indoorheat exchanger temperature and compressor operating frequency. It shouldbe noted that FIG. 4 simply represents how the rotation speed of theoutdoor fan 23 is reduced with a dotted line on a conceptual basis.Therefore, vertical plots of the dotted line are not exactly matchedwith the frequency values of the right side scale in the chart.

FIG. 4 represents that reduction in an indoor heat exchanger temperatureTi starts before the predetermined period of time TD1 is elapsed afterstart of the heating operation. The reason is that the amount of frostattaching onto the outdoor heat exchanger 13 is increased and theevaporation temperature of the refrigerant is lowered. The condensationtemperature of the refrigerant is increased when the control unit 4upgrades the present stage of the operating frequency of the compressor11 to a stage immediately higher than the present stage. This isexpressed as increase in the indoor heat exchanger temperature Ti.Suppose the control unit 4 does not increase the operating frequency ofthe compressor 11, the indoor heat exchanger temperature Ti is reducedalong the slope depicted with a dashed two-dotted line in FIG. 4.Accordingly, heating performance is also degraded.

The control unit 4 downgrades the rotation speed of the outdoor fan 23from the present level to a level immediately lower than the presentlevel in order to cancel out a partial amount of noise increased inresponse to increase in the operating frequency of the compressor 11.Such actions are repeated until start of the defrosting operationcontrol. It should be noted that the control, which is executed untilstart of the defrosting operation control after the heating operation isstarted and the predetermined period of time TD1 is further elapsed,will be hereinafter referred to as “a frost attaching conditionoperation control” for easy explanation.

<Features>

(1)

In the air conditioner 1, a determining part 43 of the control unit 4determines that the amount of frost attaching onto the outdoor heatexchanger 13 is increased when the difference between the outdoortemperature To and the outdoor heat exchanger temperature Te isincreased. Accordingly, the frost attaching condition operation controlis executed for increasing the operating frequency of the compressor 11in accordance with the reduction amount of temperature of the indoorheat exchanger 15 and for reducing the rotation speed of the outdoor fan23. The control unit 4 includes the change amounts preliminarily set forchanging the operating frequency of the compressor 11 in stages, and thechange amounts correspond to the stages on a one-to-one basis. Thecontrol unit 4 is configured to increase the operating frequency of thecompressor 11 by corresponding one of the change amounts required forupgrading the present stage of the operating frequency of the compressor11 to a stage immediately higher than the present stage every time thetemperature of the indoor heat exchanger 15 is reduced by apredetermined amount. Further, the control unit 4 is configured toreduce the rotation speed of the outdoor fan 23 in accordance with thechange amount. Consequently, degradation in heating performance, causeddue to frost attachment onto the outdoor heat exchanger, is inhibited inexecuting the heating operation. Further, noise of the compressor 11 isincreased in response to increase in the operating frequency of thecompressor 11. However, noise of the outdoor fan 23 is reduced inaccordance with reduction in the rotation speed of the outdoor fan 23.Therefore, noise increase is inhibited for the entire air conditioner 1.

(2)

In the air conditioner 1, the control unit 4 is configured to count theelapsed time TD immediately after activation of the compressor 11 andexecute the defrosting operation control for resolving a frostattachment condition of the outdoor heat exchanger 13 when the elapsedtime TD reaches the predetermined period of time TD1 during execution ofthe frost attaching condition operation control and the evaporationtemperature of the refrigerant (i.e., the outdoor heat exchangertemperature Te) becomes less than or equal to a predeterminedtemperature. Consequently, the frost attaching condition operationcontrol is configured to be executed until immediately before start ofthe defrosting operation. This makes a user or users less likely to feelthat heating is insufficient.

<First Modification>

In the aforementioned exemplary embodiment, the control unit 4 isconfigured to monitor the difference between the outdoor temperature Toand the outdoor heat exchanger temperature Te, and simultaneously,control the compressor 11 and the outdoor fan 23 in executing the frostattaching condition operation control. As an alternative method, thecontrol unit 4 may be configured to monitor the indoor heat exchangertemperature Ti, and simultaneously, control the compressor 11 and theoutdoor fan 23.

FIG. 5 is an operational flowchart from start of the heating operationcontrol to start of the defrosting operation control in an airconditioner according to a first modification of the present invention.In FIG. 5, the control unit 4 starts counting the elapsed time TD afterstart of the heating operation in Step S31. The processing then proceedsto Step S32. In Step S32, the control unit 4 keeps a standby state for apredetermined period of time (TD0) until the rotation speed of thecompressor 11 reaches a target rotation speed. The processing thenproceeds to Step S33 and the control unit 4 sets the value of a variableY to be “b”. A value, herein substituted into the variable Y, isobtained by adding a predetermined amount “t” to the indoor heatexchanger temperature Ti. However, the indoor heat exchanger temperatureTi is constant when the outdoor heat exchanger 13 is in a frost-freecondition. Therefore, the value “b” of a temperature slightly lower thanthe condensation temperature of the refrigerant is set as the initialvalue of the variable Y.

In Step S34, the control unit 4 detects the indoor heat exchangertemperature Ti through the indoor heat exchanger temperature sensor 103.The processing then proceeds to Step S35. In Step S35, the control unit4 determines whether or not the indoor heat exchanger temperature Tibecomes less than or equal to Y.

The processing then proceeds to Step S36 when the control unit 4determines the result in Step S35 as “Yes”. By contrast, the processingreturns to Step S34 when the control unit 4 determines the result inStep S35 as “No”. When the outdoor heat exchanger 13 is in a frost-freecondition, “Y=b” remains and therefore the control from Step S31 to StepS35, so-called a normal heating operation control, is continued.

In Step S36, the control unit 4 sets the variable Y to be a valueobtained by adding a predetermined amount “t” to the indoor heatexchanger temperature Ti (i.e., Ti+t). The processing then proceeds toStep S37. When the indoor heat exchanger temperature Ti becomes lessthan or equal to “b”, it is determined that the condensation temperatureis lowered due to increase in the amount of frost attaching onto theoutdoor heat exchanger 13. The control unit 4 subsequently resets thevariable Y every time the indoor heat exchanger temperature Ti isreduced by a predetermined amount “t”.

In Step S37, the control unit 4 determines whether or not the elapsedtime TD after start of the heating operation reaches the predeterminedperiod of time TD1. The processing then proceeds to Step S38 when thecontrol unit 4 determines the result in Step S37 as “Yes”. By contrast,the processing returns to Step S34 when the control unit 4 determinesthe result in Step S37 as “No”.

In Step S38, the control unit 4 increases the operating frequency of thecompressor 11 by a predetermined amount. In Step S39, the control unit 4reduces the rotation speed of the outdoor fan 23 by a predeterminedamount. In Step S40, the control unit 4 detects the outdoor temperatureTo through the outdoor temperature sensor 101. In Step S41, the controlunit 4 detects the outdoor heat exchanger temperature Te through theoutdoor heat exchanger temperature sensor 102.

In Step S42, the control unit 4 determines whether or not the outdoorheat exchanger temperature Te becomes less than or equal to a calculatedvalue (i.e., αTo−β+γ). The control unit 4 starts executing thedefrosting operation control when determining the result in Step S42 as“Yes”. By contrast, the processing returns to Step S34 when the controlunit 4 determines the result in Step S42 as “No”.

As described above, the control unit 4 can monitor the indoor heatexchanger temperature Ti, and simultaneously, control the compressor 11and the outdoor fan 23. Therefore, it is herein possible to achieve anadvantageous effect equivalent to that achieved in the aforementionedexemplary embodiment.

<Second Modification>

In the first modification, the control unit 4 is configured to monitorthe indoor heat exchanger temperature Ti, and simultaneously, controlthe compressor 11 and the outdoor fan 23. However, the control unit 4may be configured to monitor a higher side pressure Ph instead of theindoor heat exchanger temperature Ti, and simultaneously, control thecompressor 11 and the outdoor fan 23.

FIG. 6 is an operational flowchart from start of the heating operationcontrol to start of the defrosting operation control in an airconditioner according to a second modification of the present invention.In FIG. 6, the control unit 4 starts counting the elapsed time TD afterstart of the heating operation in Step S51. The processing then proceedsto Step S52. In Step S52, the control unit 4 keeps a standby state for apredetermined period of time (TD0) until the rotation speed of thecompressor 11 reaches a target rotation speed. The processing thenproceeds to Step S53 and the control unit 4 sets the value of a variableZ to be “c”. A value, herein substituted into the variable Z, isobtained by adding a predetermined amount “p” to the higher sidepressure Ph. However, the higher side pressure Ph is constant when theoutdoor heat exchanger 13 is in a frost-free condition. Therefore, thevalue “c” of a pressure slightly lower than the condensation pressure ofthe refrigerant is set as the initial value of the variable Z.

In Step S54, the control unit 4 detects the higher side pressure Phthrough a discharge side pressure sensor 111. The processing thenproceeds to Step S55. In Step S55, the control unit 4 determines whetheror not the higher side pressure Ph is less than or equal to Z.

The processing then proceeds to Step S56 when the control unit 4determines the result in Step S55 as “Yes”. By contrast, the processingreturns to Step S54 when the control unit 4 determines the result inStep S55 as “No”. When the outdoor heat exchanger 13 is in a frost-freecondition, “Z=c” remains and therefore the control from Step S51 to StepS55, so-called a normal heating operation control, is continued.

In Step S56, the control unit 4 sets the value of the variable Z to be avalue obtained by adding a predetermined amount “p” to the higher sidepressure Ph (i.e., Ph+p). The processing then proceeds to Step S57. Whenthe higher side pressure Ph becomes less than or equal to “c”, it isdetermined that the condensation pressure is reduced due to increase inthe amount of frost attaching onto the outdoor heat exchanger 13. Thecontrol unit 4 subsequently resets the variable Z every time the higherside pressure Ph is reduced by the predetermined amount “p”.

In Step S57, the control unit 4 determines whether or not the elapsedtime TD after start of the heating operation reaches the predeterminedperiod of time TD1. The processing then proceeds to Step S58 when thecontrol unit 4 determines the result in Step S57 as “Yes”. By contrast,the processing returns to Step S54 when the control unit 4 determinesthe result in Step S57 as “No”.

In Step S58, the control unit 4 increases the operating frequency of thecompressor 11 by a predetermined amount. In Step S59, the control unit 4reduces the rotation speed of the outdoor fan 23 by a predeterminedamount. In Step S60, the control unit 4 detects the outdoor temperatureTo through the outdoor temperature sensor 101. In Step S61, the controlunit 4 detects the outdoor heat exchanger temperature Te through theoutdoor heat exchanger temperature sensor 102.

In Step S62, the control unit 4 determines whether or not the outdoorheat exchanger temperature Te becomes less than or equal to a calculatedvalue (i.e., αTo−β+γ). The control unit 4 starts executing thedefrosting operation control when determining the result in Step S62 as“Yes”. By contrast, the processing returns to Step S54 when the controlunit 4 determines the result in Step S62 as “No”.

As described above, the control unit 4 can monitor the higher sidepressure Ph, and simultaneously, control the compressor 11 and theoutdoor fan 23. Therefore, it is herein possible to achieve anadvantageous effect equivalent to that achieved in the aforementionedexemplary embodiment and the first modification thereof.

Second Exemplary Embodiment

In the aforementioned exemplary embodiment and the first and secondmodifications thereof, the operating frequency of the compressor 11 isincreased, and subsequently, the rotation speed of the outdoor fan 23 isreduced. However, the operation order is not limited to the above. Forexample, the rotation speed of the outdoor fan 23 may be reduced, andthereafter, the operating frequency of the compressor 11 may be reduced.In this case, noise is reduced in response to reduction in the rotationspeed of the outdoor fan 23. Therefore, noise is still acceptable by thereduction amount. Subsequently, the operating frequency of thecompressor 11 is increased by the amount corresponding to the acceptablerange of noise increase while monitoring is executed for the indoor heatexchanger temperature Ti, the higher side pressure Ph or the differencebetween the outdoor temperature To and the outdoor heat exchangertemperature Te. With the control, noise is kept constant in the entireair conditioner 1. The following will be explained with reference toFIGS. 7 and 8.

FIG. 7 is a chart representing the relation among elapsed time afterstart of the heating operation, indoor heat exchanger temperature andcompressor operating frequency in an air conditioner according to asecond exemplary embodiment. In FIG. 7, the rotation speed of theoutdoor fan 23 is reduced to a predetermined rotation speed when it isdetermined that frost attaches onto the outdoor heat exchanger 13 andthe elapsed time TD reaches the predetermined period of time TD1 afterstart of the heating operation.

Accordingly, noise due to the outdoor fan 23 is reduced and noise isthereby still acceptable by the reduction amount. Subsequently, theindoor heat exchanger temperature Ti is monitored, and simultaneously,the operating frequency of the compressor 11 is increased by the amountcorresponding to the acceptable range of noise increase when the indoorheat exchanger temperature Ti is reduced by ΔT. Thus, the indoor heatexchanger temperature Ti is kept roughly constant. It should be notedthat ΔT is preferably equal to “3K”.

The control unit 4 includes the change amounts preliminarily set forchanging the operating frequency of the compressor 11 in stages. Thechange amounts correspond to the stages on a one-to-one basis. Inincreasing the operating frequency of the compressor 11, the controlunit 4 is configured to increase the operating frequency of thecompressor 11 by corresponding one of the change amounts required forupgrading the present stage of the operating frequency of the compressor11 to a stage immediately higher than the present stage.

<Modification>

Further, FIG. 8 is a chart representing the relation among elapsed timeafter start of the heating operation, higher side pressure andcompressor operating frequency in an air conditioner according to amodification of the second exemplary embodiment. In FIG. 8, the rotationspeed of the outdoor fan 23 is reduced to a predetermined rotation speedwhen it is determined that frost attaches onto the outdoor heatexchanger 13 and the elapsed time TD after start of the heatingoperation reaches the predetermined period of time TD1.

Accordingly, noise due to the outdoor fan 23 is reduced and noise isthereby still acceptable by the reduction amount. Subsequently, thehigher side pressure Ph is monitored, and simultaneously, the operatingfrequency of the compressor 11 is increased by the amount correspondingto the acceptable range of noise increase when the higher side pressurePh is reduced by ΔP. Accordingly, the higher side pressure Ph is keptroughly constant. It should be noted that ΔP is preferably equal to 0.2MPa.

As described above, not only noise is kept constant in the entire airconditioner 1 but also excessive degradation in heating performance isinhibited in the second exemplary embodiment and the modificationthereof

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the frostattaching condition operation control inhibits degradation in heatingperformance in a period of time when the heating performance is normallydegraded due to frost attachment. Therefore, the present invention isuseful for the general air conditioners using the vapor compressionrefrigeration cycle.

REFERENCE SIGNS LIST

-   1 Air conditioner-   4 Control Unit-   11 Compressor-   13 Outdoor heat exchanger-   14 Expansion valve (Decompressor)-   15 Indoor heat exchanger-   23 Outdoor fan-   43 Determining part-   101 Outdoor temperature sensor (First temperature sensor)-   102 Outdoor heat exchanger temperature sensor (Second temperature    sensor)-   103 Indoor heat exchanger temperature sensor (Third temperature    sensor)

CITATION LIST Patent Literature

-   PTL 1: Japan Laid-open Patent Application Publication No.    JP-A-S62-069070

1. An air conditioner using a vapor compression refrigeration cycle inwhich a refrigerant is sequentially circulated through a compressor, anindoor heat exchanger, a decompressor and an outdoor heat exchangerduring execution of a heating operation, the air conditioner comprising:an outdoor fan configured to blow the outdoor heat exchanger; and acontrol unit including a determining part configured to determinewhether or not an amount of frost attaching onto the outdoor heatexchanger is increased during execution of the heating operation, thecontrol unit configured to control an operating frequency of thecompressor and a rotation speed of the outdoor fan, the control unitbeing further configured to reduce the rotation speed of the outdoor fanwhen the determining part determines that the amount of frost attachingonto the outdoor heat exchanger is increased, and execute a frostattaching condition operation control in order to increase the operatingfrequency of the compressor either simultaneously with reducing therotation speed of the outdoor fan or when a predetermined performancedegradation is substantially caused after reducing the rotation speed ofthe outdoor fan.
 2. The air conditioner recited in claim 1, wherein thecontrol unit is further configured to reduce the rotation speed of theoutdoor fan in accordance with an increase amount of the operatingfrequency of the compressor during execution of the frost attachingcondition operation control.
 3. The air conditioner recited in claim 1further comprising: a first temperature sensor configured to detect anoutdoor temperature; and a second temperature sensor configured todetect a temperature of the outdoor heat exchanger, the control unitbeing further configured to monitor a difference between a valuedetected by the first temperature sensor and a value detected by thesecond temperature sensor, and determine that the amount of frostattaching onto the outdoor heat exchanger is increased when thedifference is increased.
 4. The air conditioner recited in claim 3,further comprising: a third temperature sensor configured to detect atemperature of the indoor heat exchanger, the control unit being furtherconfigured to monitor the temperature of the indoor heat exchanger withthe third temperature sensor, and increase the operating frequency ofthe compressor in accordance with a reduction amount of the temperatureof the indoor heat exchanger during execution of the frost attachingcondition operation control.
 5. The air conditioner recited in claim 4,wherein the control unit has change amounts preliminarily set in orderto change the operating frequency of the compressor in stages, thechange amounts corresponding to the stages on a one-to-one basis, andthe control unit is further configured to control the operatingfrequency of the compressor to be increased by corresponding one of thechange amounts required to upgrade a present stage of the operatingfrequency of the compressor to a stage immediately higher than thepresent stage every time the temperature of the indoor heat exchanger isreduced by a predetermined amount.
 6. The air conditioner recited inclaim 3, further comprising: a pressure sensor disposed on a dischargeside of the compressor, the pressure sensor being configured to detect ahigher side pressure, the control unit being further configured tomonitor the higher side pressure with the pressure sensor, and increasethe operating frequency of the compressor in accordance with a reductionamount of the higher side pressure during execution of the frostattaching condition operation control.
 7. The air conditioner recited inclaim 6, wherein the control unit has change amounts preliminarily setin order to change the operating frequency of the compressor in stages,the change amounts corresponding to the stages on a one-to-one basis,and the control unit is further configured to control the operatingfrequency of the compressor to be increased by corresponding one of thechange amounts required to upgrade a present stage of the operatingfrequency of the compressor to a stage immediately higher than thepresent stage every time the higher side pressure is reduced by apredetermined amount.
 8. The air conditioner recited in claim 1, whereinthe control unit is further configured to count an elapsed time afteractivation of the compressor, and execute a defrosting operation controlin order to resolve frost attachment onto the outdoor heat exchangerwhen the elapsed time reaches a predetermined period of time duringexecution of the frost attaching condition operation control while anevaporation temperature of the refrigerant reaches a predeterminedtemperature.
 9. The air conditioner recited in claim 2, furthercomprising: a first temperature sensor configured to detect an outdoortemperature; and a second temperature sensor configured to detect atemperature of the outdoor heat exchanger, the control unit beingfurther configured to monitor a difference between a value detected bythe first temperature sensor and a value detected by the secondtemperature sensor, and determine that the amount of frost attachingonto the outdoor heat exchanger is increased when the difference isincreased.
 10. The air conditioner recited in claim 9, furthercomprising: a third temperature sensor configured to detect atemperature of the indoor heat exchanger, the control unit being furtherconfigured to monitor the temperature of the indoor heat exchanger withthe third temperature sensor, and increase the operating frequency ofthe compressor in accordance with a reduction amount of the temperatureof the indoor heat exchanger during execution of the frost attachingcondition operation control.
 11. The air conditioner recited in claim10, wherein the control unit has change amounts preliminarily set inorder to change the operating frequency of the compressor in stages, thechange amounts corresponding to the stages on a one-to-one basis, andthe control unit is further configured to control the operatingfrequency of the compressor to be increased by corresponding one of thechange amounts required to upgrade a present stage of the operatingfrequency of the compressor to a stage immediately higher than thepresent stage every time the temperature of the indoor heat exchanger isreduced by a predetermined amount.
 12. The air conditioner recited inclaim 9, further comprising: a pressure sensor disposed on a dischargeside of the compressor, the pressure sensor being configured to detect ahigher side pressure, the control unit being further configured tomonitor the higher side pressure with the pressure sensor, and increasethe operating frequency of the compressor in accordance with a reductionamount of the higher side pressure during execution of the frostattaching condition operation control.
 13. The air conditioner recitedin claim 12, wherein the control unit has change amounts preliminarilyset in order to change the operating frequency of the compressor instages, the change amounts corresponding to the stages on a one-to-onebasis, and the control unit is further configured to control theoperating frequency of the compressor to be increased by correspondingone of the change amounts required to upgrade a present stage of theoperating frequency of the compressor to a stage immediately higher thanthe present stage every time the higher side pressure is reduced by apredetermined amount.
 14. The air conditioner recited in claim 2,wherein the control unit is further configured to count an elapsed timeafter activation of the compressor, and execute a defrosting operationcontrol in order to resolve frost attachment onto the outdoor heatexchanger when the elapsed time reaches a predetermined period of timeduring execution of the frost attaching condition operation controlwhile an evaporation temperature of the refrigerant reaches apredetermined temperature.
 15. The air conditioner recited in claim 3,wherein the control unit is further configured to count an elapsed timeafter activation of the compressor, and execute a defrosting operationcontrol in order to resolve frost attachment onto the outdoor heatexchanger when the elapsed time reaches a predetermined period of timeduring execution of the frost attaching condition operation controlwhile an evaporation temperature of the refrigerant reaches apredetermined temperature.